Plastic bag having reinforced closure

ABSTRACT

A plastic bag having formed integrally therewith cooperating male and female pressure fastenable releasable interlocking elements for selectively closing the open end of the bag and a pair of stiffener ribs also formed integrally with the bag but of a thermoplastic material more rigid than that from which the remainder of the bag is formed to provide increased lateral rigidity along the open end of the bag to prevent inadvertent separation of the interlocking elements.

United States Patent [72] In ent Steven Allsllil 2,746,502 5/1956 Graell150/3 11 E- 61st New York, 10021 3,198,228 8/1965 Naito 150/3 [21] Appl.No. 779,383 3,338,284 8/1967 Ausnit..... 150/3 [22] Filed d g a 1 3?3,338,285 8/1967 Jaster 150/3 t [45] Pate e e Primary Examiner-Donald F.Norton Attorney-Hill, Sherman, Meroni, Gross & Simpson [5 4] PLASTIC BAGHAVING REINFORCED CLOSURE 8 Claims, 5 Drawing Figs. [52] US. Cl 150/3BST C A plastic bag having f d integrally therewith f 365d 33/02.cooperating male and female pressure fastenable releasable [50] Fieldol'search 150/3, interlockingelemems for selectively closing the openend of 24/2013 the bag and a pair of stiffener ribs also fonnedintegrally with the bag but of a thermoplastic material more rigid thanthat [56] References C'ted from which the remainder of the bag is formedto provide in- UNITED STATES PATENTS creased lateral rigidity along theopen end of the bag to 2,l 4 4 75 5 1/1939 Freedman prevent inadvertentseparation of the interlocking elements.

1 PLASTIC BAG HAVING REINFORCED CLOSURE BACKGROUND OF THE INVENTION Thisinvention pertains generally to the field of plastic containers such asbags, pouches or the like and more particularly to such containers whichinclude a pair of superimposed plastic sheets joined together along theedges thereof except for a portion forming the open side of the bag andwhich further include cooperating male and female pressure fastenablereleasable interlocking elements made of plastic and formed integrallywith the sheets along the openside of the bag.

Such containers are known in the prior art as having utility in a widevariety of applications. For example, such containers are used asinexpensive, light briefcases. They are also used as packages for a widevariety of goods. Such diverse products as handkerchiefs, fishhooks andnuts and bolts are all packaged in such plastic containers.

Examples of early prior art plastic bags having releasable fasteners aregenerally formed in two parts, i.e., a pair of superimposedplasticsheets bonded together along their correspo'ndingedges except forthe edge along which is formed the open end of the bag, and a pair ofplastic strips on which are formed the interlocking profiles or thecooperating male and female elements of the releasable fastener. The twostrips are usually heat-sealed to the sheets along the open side of thebag. In other examples of the prior art a single sheet of plasticmaterial is folded over itself toform the opposite walls of the bag butin other respects the construction of. the bag is similar to thefirst-mentioned example. 1

With respect to either of these two bagconstructions it is es- .sentialthat the plastic sheets be of sufficient thickness to allow theefficient heat-sealing operation of the fastener strips to the sheets.As a consequence the sheets which form the sides of the bag are oftenthicker than the particular packaging appli cation requires. Forexample, assume that a plastic bag in which a handkerchief is intendedto be packaged requires a wall thickness'of only 0.2 mils. Nevertheless,it may often be necessary to increase the wall thickness by 50 to 100percent of the thickness required by the goods in order to allow thesheets to be sealed quickly and adequately to the fastener strips.

The interlocking male and female elements of the releasable fastenerwere and are relatively small and quite flexible so that the releasablefastener can be opened and closed quite easily and with only lightfinger pressure. 1

More recently it was determined that plastic bags can be formed from anextruded tubular plastic'film, the operating male and female elements ofthe fastener being formed integrally with the film. In this operationthe tubular film is slit longitudinally, generally between the male andfemale fastener elements or profiles, and then the film is cut along itslength into sections of predetermined length and bonded generally at thesame time as the cutting, along the cut edges to form a plurality ofindividual containers. As a result of the integral formation of thefastener profiles or male and'female interlocking elements the thicknessof the sheets which comprise the walls of the bag can usually be reducedto the thickness that is required or dictated by the product or goodswhich are to be contained within the bag.

All of these prior art plastic bags, however, because of the low rangeof thicknesses of the plastic sheets which comprise the walls of thebag, have been found to be susceptible to inadvertent opening of thereleasable fastener. This susceptibility arises from the lack ofsufficient lateral rigidity of the bag which is larger than the curve ofthe adjacent portion of the other element, and since the elements are ofthe same length under normal conditions, the result of this curvature ordoubling-up is that the elements become separated from one another. Thisseparation of the two elements of the fastener has the effect, ofcourse',,of inadvertently opening the bag.

SUMMARY OF THE INVENTION In light of the foregoing it is an object ofthe present invention to provide a plastic bag in which the plasticfastener attached to the walls of the bag whether integrally atextrusion or later by sealing, is reinforced in a manner so as toincrease the lateral rigidity of the bag along the closeable end and todecrease the likelihood of inadvertent opening of the releasablefastener when the bag is subjected to side forces.

To this end the invention may be summarized as comprising a plastic bag(and a method of and apparatus for producing the same) which comprises apair of superimposed plastic sheets which form the walls of the bag anda plastic releasable fastener formed of cooperating interlocking maleand female elements made either separately or integrally with the sheetsand extending continuously along the open side of the bag. A stiffenerrib or beam is also formed integrally with one or both of the plasticfasteners or sheets and extends along the open end of the bag to providelateral rigidity and to reduce the likelihood of inadvertent opening ofthe releasable fastener when the bag is subjected to lateral or sideforces tending to wrinkle or double-up the fastener.

The rib (or ribs) is alsoformed of plastic material but in the preferredembodiment the plastic of which the rib is made is considerablyphysically stiffer than is the plastic of which the sheets and thefastener are made.

.In the preferred embodiment the bag is'formed from an extruded tubularfilm, though it may also be formed from an exthe invention, of verystiff plastic.

As a consequence of the stiffener rib or ribs, a plastic bag constructedin accordance with the principles of the present invention is morereliable in use as a container because of the reduced likelihood ofinadvertent opening of the fastener when subjected to lateral forcesacting onthe bag along a line parallel to the longitudinal axes of themale and female fastener elements.

Another object of the present invention is to provide an improvedplastic bag at substantially the same cost as is required in theproduction of prior art plastic bags.

Another object of the invention is to rigidify the bag in the area ofthe releasable fastener for reducing the likelihood of inadvertentopening of the fastener when the bag is subjected to side forces.

Another object is to provide a bag with a reinforcing'or rigidifying ribor beam in an inexpensive manner through the utilization of a plasticmaterial of greater stiffness than the plastic material of which thewalls of the bag and the releasable fastener are formed. Many otherfeatures, advantages and additional objects of the present inventionwill become manifest to those versed in the art upon making reference tothe detailed description which follows and the accompanying sheets ofdrawings, in which preferred structural embodiments incorporating theprinciples of thepresent'invention are shown by way of illustrativeexample only.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an isometric view of aplastic container such as a bag, pouch or the like constructed inaccordance with the principles of the present invention.

FIG. 2 is an enlarged cross-sectional view taken along lines ll-ll ofFIG. 1.

FIGS. 3 and 4 are similar to FIG. 2 but illustrate other forms of theinvention.

FIG. 5 comprises a plastic extruder assembly constructed in accordancewith the principles of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description ofthe invention the same reference numerals are used throughout indesignating the various parts or features of the invention which arecommon to the several illustrated forms thereof.

Referring to the drawing and particularly to FIGS. 1 and 2, referencenumeral indicates generally a plastic bag or similar container such as abriefcase, pouch or the like constructed in accordance with theprinciples of the present invention. The bag 10 generally comprises apair of plastic sheets 11 and 12 which are superimposed one on the otheror otherwise arranged in substantially parallel side-by'side relation.In the illustrated embodiment sheets 11 and 12 are rectangularly shapedalthough it will be understood as the description of the inventiondevelops herein that the sheets 1 1 and 12, which comprise oppositewalls of the bag 10, may assume configurations other than therectangular.

The adjacent or corresponding edges of the sheets 11 and 12 are joinedtogether along the lines indicated at reference numerals 13, 14 and butare separated along a top open end of the bag indicated at 16. The edges13 and 14 may be bonded together by means of a heat seal, adhesive orthe like. The bottom edge 15 may also comprise a bond between sheets 11and 12 but in the illustrated embodiment of the invention as in FIG. 2the sheets 11 and 12 actually comprise a single larger sheet which isfolded back over itself to provide an integral bottom wall at the loweredge 15.

The bag 10 may be further characterized as comprising a pressurereleasable fastener indicated generally at reference numeral 17 which isformed parallel and close to the top open end 16. The fastener 17comprises a pair of cooperating interlocking profiles or rib and groovemembers, one of which may be referred to as a male element and which isindicated at reference numeral 18 and the other of which may be referredto as a female element and which is indicated at reference numeral 19.The male and female elements 18 and 19 as shown in their preferredembodiment are formed integrally with sheets 11 and 12 and projectperpendicularly thereto. In addition the male and female elements 18 and19 extend in straight lines substantially across the entire width of thesheets 11 and 12.

Sheets 11 and 12 and the male and female elements 18 and 19 are formedof the same thermoplastic material which may be characterized as beingquite flexible. This flexibility enables the fastener 17 to be openedand closed easily without any appreciable force.

Thus in order to close the fastener 17 a slight pressure is applied tothe male and female elements 18 and 19 to force the same together alongthe length of the fastener 17. This pressure causes a tapered arrowheadportion 18 of the male element 18 to spread a pair of arms 20 and 21formed on the female element 19. After the arrowhead portion 18 iscompletely inserted into a recess 22 formed between the arms 20 and 21,the inherent resiliency of the thennoplastic causes the arms to intumover and become interlocked with the arrowhead portion 18.

To open the fastener 17 it is merely necessary to apply a slightseparating force to marginal portions 23 and 24 of the sheets 11 and 12which extend adjacent the open end 16. The application of this forcecauses the arm 20 to spread and allow the separation of the arrowheadportion 18' of the male element 18 from the female element 19, thusopening the top end 16 ofthe bag 10.

As a result of the high flexibility of the thermoplastic of which thesheets 11 and 12 and the fastener 17 are constructed the upper portionof the bag 10 adjacent the top open end 16 may be easily collapsed orsqueezed together in serpentine fashion by the application of a lateralforce acting along the longitudinal axes of the male and female elements18 and 19. The application of such a lateral force may be inadvertent,such as may occur, for example, if the bag were to fall to the ground onedges 13 or 14. In addition, however, the normal use of the bag 10 inthe performance of its function as a container may involve inadvertentor unavoidable lateral contraction of the bag along its top end 16.

The resultant doubled up" or curved configuration of the fastener 17causes separation of the male and female elements 18 and 19. Since themale and female elements 18 and 19 are of the same length and arecontinuous across the entire width of the sheets 11 and 12, a curvatureof the fastener 17 will produce different radii of correspondinglongitudinal portions of the male and female elements 18 and 19. Sincethe plastic of which the sheets 11 and 12 and the male and femaleelements 18 and 19 are constituted has virtually no stretch capabilitythe result of this difference in curvature of the male and femaleelements is the separation of the two and opening of the fastener 17.

This problem could perhaps be overcome by forming the male and femaleelements 18 and 19 of very rigid thermoplastic material. While thiswould provide the lateral rigidity to the fastener 17 necessary toreduce or substantially eliminate bending of the fastener upon theapplication of moderate side forces, nevertheless as a result of thisincreased rigidity it then would be extremely difficult to lock andunlock the male and female elements. A compressive force substantiallygreater than moderate finger force would be required and for manyapplications of the bag 10 this additional force required to open andclose the bag would be prohibitively undesirable.

In accordance with the present invention, the lateral rigidity of thebag 10 (at least along that portion thereof which may effeet theinadvertent opening of the fastener 17) is increased by the utilizationof a reinforcement beam or stiffener rib extending substantially acrossthe width of the bag 10. In FIG. 2 a stiffener rib is indicated atreference numeral 25, the same being constructed integrally with thesheet 12 and formed of thermoplastic material which is much stiffer andmore rigid than the thennoplastic material of which the sheets 11 and 12and the male and female elements 18 and 19 are constructed. As indicatedanother stiffener rib 26 may be formed on the sheets 11, and both ribs25 and 26 project perpendicularly for m the sheets 11 and 12 and extendin spaced parallel relation to the male and female elements 18 and 19 ofthe fastener 17. The stiffener ridges or ribs 25 and 26 are shown intheir preferred embodiment on the inside of the bag. They may howeveralso be located on the outside of the bag 10.

With the provision of the stiffener ribs 25 and 26, assume that alateral force were applied to the bag 10 against the edges 13 and 14.While the bag may become contracted or doubled up in the central orlower portions thereof, that portion of the bag which is adjacent thetop end 16 and which includes the fastener 17 and the stiffener ribs 25and 26 is maintained in a stiff or rigid position, or at least in abroad curved position, so as to reduce or entirely eliminate doubling-upof the upper portion in a serpentine fashion to a degree sufficient toseparate the male and female elements 18 and 19.

In the embodiment illustrated in FIG. 2 the stiffener ribs 25 and 26 aresubstantially rectangularly shaped in transverse cross section, that is,a cross-sectional view through the bag 10 in a direction normal to thesheets 11 and 12. The ribs 25 and 26 are also slightly offset from oneanother in a direction parallel to the sheets 11 and 12 and, in theclosed position of the fastener 17, are arranged in mutually overlappingrelation.

In the embodiment illustrated in FIG. 3 the stiffener ribs 25a and 26aare hook-shaped and are arranged in mutually inverted relation toprovide an interlocking connection therebetween when they are pressedtogether in a direction normal to the sheets 11 and 12, which is thesame direction in which the force is applied to close the fastener 17.

In the embodiment illustrated in FIG. 4, the ribs 25b and 26b eachcomprise in transverse cross section a first portion 27 which projectslaterally from its corresponding sheet 11 and 12 and a second portion 28which extends from the distal end of the first portion 27 in a directionparallel to its corresponding sheet. In this embodiment as in theembodiment illustrated in FIG. 3, the ribs 25b and 26b are arranged inmutually inverted relation with portions 28a and 28b overlapping oneanother to provide an interlocking connection therebetween when they arepressed together in a direction normal to the sheets 11 and 12.Depending on the length of the portions 28a and 28b and as theseportions are rigid, it may be necessary to interhook them rather thanpress them into.

position.

The present invention also encompasses a method of making the bag and anapparatus useful in the practice of that method.

In the preferred method a circumferentially continuous'tubular film ofthermoplastic is extruded froma die. Formed in the walls of the dieplate which form the annular aperture through which the tubular film isextruded area plurality of recesses which are shaped to correspond to.the male and female elements 18 and 19 and to the stiffener ribs and 26.The continuously extruded tubular film issubsequently cut along itslength into plural sections. The longitudinal length of each sectioncorresponds to a predetermined width of a plastic bag, that is, thedistance between edges 13 and 14 of the bag 10. The film is firstflattened andv thencut. longitudinally between the male andfemaleelements 18 and 19 so that one half of the slit film overlies the otherhalf in a manner so that sheet 11 is superimposed on sheet 12 as inFIGS. 2-4. The cut edges of each section are then bonded to complete thebags.

Illustrated in FIG. 5 is a die assembly indicated generally at referencenumeral 29 which is constructed in accordance with the preferred methodof the present invention of forming a tubul'ar film having the male andfemale elements '18 and 19 and the stiffener ribs 25 and 26integral'therewith. The extrusion die assembly 29 may be moreparticularly characterized as comprising a die plate 30 in which anannular aperture 31 is formed. Although the die plate 30 is illustratedin FIG. 5 as being two-dimensional it will be understood that it doeshave a dimension perpendicular to the plane of the drawing and theaperture 31 extends longitudinally into the die plate 30.

t The aperture 31 is formed between a pair of circular walls 32 and 33,and formed in the wall 32 are a plurality of recesses indicated atreference characters 18",19, 25", and 26". These recesses, of course,conform to and correspond with the male and female elements 18 and 19and the stiffener ribs 25 and 26. All of the recesses are'at a specificpoint in open communication with the aperture 31.

The assembly 29 also comprises a conduit indicated somewhatschematically at reference numeral 34 adapted for connection to a sourceof thermoplastic for delivering the thermoplastic continuously in thedirection of the arrow 35 to the annular aperture 31. The resultanttubular film is extruded form the aperture 31 in a directionperpendicular to the plane of the drawing.

The thermoplastic being delivered through conduit 34 will enter therecesses 18"- and 19" opening into the aperture 31 thereby causing themale and female elements 18 and 19 to be extruded integrally with thetubular film and of the same therrnoplastic of which the film is made.Another conduit indicated generally schematically at reference numeral36 is also adapted for connection to a source of thermoplastic fordelivery thereof in the direction of the arrow indicated at reference37. The thermoplastic being delivered by conduit 36, however, is not thesame as that which is delivered by conduit 34 and in fact is much morerigid or stiff when cooled to its solid state. Preferably thethermoplastic being delivered through conduit 36 is the most rigid orstiff polyethylene which is capable of being extruded through therecesses 25" and 26".

Passages 38 and 39 interconnect the conduit 36 with the recesses 25" and26" so that the thermoplastic from conduit 34 will form that portion ofthe tubular film immediately adjacent ribs 25 and 16 and will join withthe more rigid plastic coming from conduits 38 and 39 to form the ribs25 and 26 in overlying relation on the film.

It will be appreciated that after the tubular film emerges from theextrusion die plate 30 and the temperature thereof has fallen to asufficient degree, the film has been slit longitudinally between themale and female elements 18 and 19, cut into sections along the lengththereof and bonded along the cut edges, it will form a plurality of bagssimilar to those indicated at reference numeral 10.

Although minor modifications might be suggested by those versed in theart, it should be understood that I wish to embody within the scope ofthe patent warranted hereon all such modifications as reasonably comewithin the scope of my contribution to the art. Y

Iclaim:

l. A plastic bag including a pair of superimposed sheet portions thecorresponding edges of which are bonded together to form sealed sidesand an open side,

means forming longitudinally continuous cooperating male and femaleinterlocking elements on said sheets along the open side of the bag toprovide a releasable fastener, and

a stiffener rib formed on one of said sheets extending along the openside of said bag,-

said male and femaleelements being formed of a first thermoplasticmaterial and said stiffener rib being formed of a second thermoplasticmaterial, said second thermoplastic material being substantially morerigid than said first thermoplastic material to provide lateral rigidityto saidxbag along the open side to reduce the likelihood of inadvertentopening of said releasable fastener. 1 I I 2. The plastic bag as definedin. claim 1, wherein said cooperating male and female elements and saidstiffener rib are formed integrally withsaid plastic sheets.

3. The plastic bag as defined in claim 2, wherein said stiffener rib isdis'posedin spaced parallel relation with respect to said cooperatingmale and female elements.

4. The plastic bag as defined in claim 3, and including anotherstiffener rib formed on the other of said sheet and extending along theopen side of said bag in parallel relation to said first mentionedstiffener rib, I

said ribs being slightly offset from one another in a direction parallelto said sheets and arranged in mutually overlapping relation in theclosed position of said fastener. 5. The plastic bag as defined in claim4, said ribs being substantially rectangularly shaped in transversecross section.

6. The plastic bag as defined in claim 1, and including anotherstiffener rib of said second thermoplastic material formed on the otherof said sheets and extending along the open side of said bag in parallelrelation to said first-mentioned stiffener rib,

said ribs being hook-shaped in transverse cross section and arranged inmutually inverted relation to provide an interlocking connectiontherebetween when joined together.

7. The plastic bag as defined in claim 1, and including anotherstiffener rib of said second thermoplastic material formed on the otherof said sheets and extending along the open side of said bag in parallelrelation to said first mentioned rib, said ribs each comprising intransverse cross section a first portion projecting laterally of itscorresponding sheet and a second portion extending from the distal endof said first portion in a direction parallel to its correspondingsheet, said ribs being arranged in mutually inverted relation and saidsecond portions overlapping one another to provide an interlockingconnection therebetween when joined together.

8. In a bag having sides made of plastic sheet-form material and anelongated plastic releasable fastener joined along correspondingmarginal portions of the bag sides to provide a closable opening in thebag, the improvement comprising stiffening means formed adjacent saidreleasable fastener to impart lateral rigidity to the marginal portionsbeyond 7 sides,

said rib being made of plastic having a stiffness value which is greaterthan the stiffness value of the plastic of which the bag sides and thereleasable fastener are made.

1. A plastic bag including a pair of superimposed sheet portions thecorresponding edges of which are bonded together to form sealed sidesand an open side, means forming longitudinally continuous cooperatingmale and female interlocking elements on said sheets along the open sideof the bag to provide a releasable fastener, and a stiffener rib formedon one of said sheets extending along the open side of said bag, saidmale and female elements being formed of a first thermoplastic materialand said stiffener rib being formed of a second thermoplastic material,said second thermoplastic material being substantially more rigid thansaid first thermoplastic material to provide lateral rigidity to saidbag along the open side to reduce the likelihood of inadvertent openingof said releasable fastener.
 2. The plastic bag as defined in claim 1,wherein said cooperating male and female elements and said stiffener ribare formed integrally with said plastic sheets.
 3. The plastic bag asdefined in claim 2, wherein said stiffener rib is disposed in spacedparallel relation with respect to said cooperating male and femaleelements.
 4. The plastic bag as defined in claim 3, and includinganother stiffener rib formed on the other of said sheet and extendingalong the open side of said bag in parallel relation to said firstmentioned stiffener rib, Said ribs being slightly offset from oneanother in a direction parallel to said sheets and arranged in mutuallyoverlapping relation in the closed position of said fastener.
 5. Theplastic bag as defined in claim 4, said ribs being substantiallyrectangularly shaped in transverse cross section.
 6. The plastic bag asdefined in claim 1, and including another stiffener rib of said secondthermoplastic material formed on the other of said sheets and extendingalong the open side of said bag in parallel relation to saidfirst-mentioned stiffener rib, said ribs being hook-shaped in transversecross section and arranged in mutually inverted relation to provide aninterlocking connection therebetween when joined together.
 7. Theplastic bag as defined in claim 1, and including another stiffener ribof said second thermoplastic material formed on the other of said sheetsand extending along the open side of said bag in parallel relation tosaid first mentioned rib, said ribs each comprising in transverse crosssection a first portion projecting laterally of its corresponding sheetand a second portion extending from the distal end of said first portionin a direction parallel to its corresponding sheet, said ribs beingarranged in mutually inverted relation and said second portionsoverlapping one another to provide an interlocking connectiontherebetween when joined together.
 8. In a bag having sides made ofplastic sheet-form material and an elongated plastic releasable fastenerjoined along corresponding marginal portions of the bag sides to providea closable opening in the bag, the improvement comprising stiffeningmeans formed adjacent said releasable fastener to impart lateralrigidity to the marginal portions beyond that afforded by the inherentrigidity of the sides of the bag and by the releasable fastener, saidstiffening means comprising a rib formed on the marginal portion of oneof the bag sides and extending in parallel relation to the releasablefastener and projecting toward the marginal portion of the other of thebag sides, said rib being made of plastic having a stiffness value whichis greater than the stiffness value of the plastic of which the bagsides and the releasable fastener are made.